1. Field of the Invention
The present invention relates generally to radio communication apparatus, such as a mobile radio telephone apparatus. More particularly, the invention relates to a radio communication apparatus operative to control a transmissible signal, which is produced by modulating a carrier signal with a communications signal, so as to have an appropriate degree of modulation thereof or an appropriate output level thereof and then to transmit the transmissible signal controlled in its degree of modulation or its output level.
2. Description of the Prior Art
In a cellular mobile telephone system, communications between a mobile telephone apparatus such as a mobile radio telephone apparatus mounted in an automobile and an ordinary telephone subscriber, or between automobile mounted mobile telephone apparatus, are carried out through a particular local base station. A radio communication apparatus constituting the mobile radio telephone apparatus used in the public mobile telephone system is operative to transmit not only a voice information signal but also various control tone signals and control data. In transmissions of the voice information signal, control tone signals and control data, transmissible signals are produced by, for example, frequency-modulating a common carrier with the voice information signal, control tone signals and signals representing the control data (control data signals), respectively, and each of the transmissible signals thus produced is transmitted. In such transmissions, the transmissible signals formed based on the voice information signal, control tone signals and control data signals are provided with respective degrees of modulation which have been standardized to be different from each other. Further, each of the transmissible signals is transmitted through a power amplifier to have a predetermined output level which has been also standardized.
Accordingly, the radio communication apparatus which constitutes the mobile radio telephone apparatus used in the public mobile telephone system is required to produce various transmissible signals, each of which is obtained by frequency-modulating a predetermined carrier with one of the voice information signal, control tone signals and control data signals, and provided with degree of modulation which meets standard requirements, and to control each of the transmissible signals to have an output level which also meets standard requirements, before transmission of each of the transmissible signals.
The degree of modulation of the transmissible signal is determined by adjusting the level of the voice information signal, control tone signal, or control data signal with which the carrier is frequency-modulated to produce the transmissible signal. The output level of the transmissible signal is determined by adjusting a level of a detected output obtained from a level detector. The arrangement includes a power amplifier for amplifying the power of the transmissible signal and a level controller provided for controlling the power amplifier in view of a comparison output obtained by comparing the level of the detection output from the level detector with a reference level.
In the previously proposed radio communication apparatus, adjustment in the levels of each of the voice information signal, control tone signals, and control data signals is carried out by adjusting a variable resistor disposed on a signal path for each of the voice information signal, control tone signals, and control data signals. Adjustment in the output levels of the detected output from the level detector, provided for detecting the level of each of the transmissible signals amplified by the power amplifier, is carried out for determining the output level of each of the transmissible signals also in the production process of the apparatus by adjusting a resistance value of a variable resistance connected to an output end of the level detector.
The above-mentioned adjustment in level of each of the voice information signal, control tone signals, and control data signals and adjustment in level of the detected output from the level detector bring about a problem that complicates work resulting in relatively large Working hours required to adjust correctly the adjustable resistors for determining the degree of modulation of each of the transmissible signals and the output level of each of the transmissible signals.
Further, in the case where the resistance value of the variable resistance disposed on the signal path for each of the voice information signal, control tone signals, and control data signals and the resistance value of the variable resistance connected to the output of the level detector accompanying the power amplifier is adjusted, to set the degree of modulation and output level of each of the transmissible signals before a printed circuit board on which the variable resistors are mounted is installed in the apparatus, the degree of modulation or of each of the transmissible signals can be subtly varied so as to have undesirable deviations when the printed circuit board on which the variable resistors are mounted is installed in the apparatus. If the degree of modulation or the output level of each of the transmissible signals is undesirably varied when the printed circuit board is installed in the apparatus, the resistance value of each of the variable resistors must be adjusted again so as to correct the undesirable variation after the printed circuit board is installed in the apparatus. This result is disadvantageous in that production efficiency of the apparatus is decreased, because adjustments to the resistors must be made twice.